In the simplest expression of GHD, we consider a system, composed of many particles in interaction, which has the property of integrability. The system can be either quantum or classical, but the theory was initially developed to discuss the quantum case in the original works [1]} and [2]}. This includes the Lieb-Liniger model, considered in [1]}, which will be our main example. Additionally, there is no need to restrict to systems of particles, and the Heisenberg spin chain was considered in [2]}.
